I. Field of the Invention
This invention relates to blind fasteners for securing sheet material and, in particular, to a blind fastener with a self-expanding sleeve having a mechanical lock to prevent loosening of the fastener.
II. Description of the Prior Art
Blind fasteners have become particularly useful in securing sheet materials where it is impossible to access the underside of the material. Typically such fasteners are inserted into an aperture through the material and include a threaded stem for engaging the fastener. Rotation of the stem draws an expansion member into engagement with the underside of the material. Expansion may be aided by a nut body which forces the expansion member radially outwardly to engage the underside. Upon complete expansion to fully clamp the sheet material, the exterior end of the threaded stem may be broken away to eliminate any protrusions from the exterior surface.
Such fasteners have wide application in aircraft and space vehicle assembly. However, the vibrations and sonic fatigue such vehicles are subject to cause loosening of the fastener. Various locking features have been incorporated into such fasteners with various degrees of success. Although it is desirable to ensure locking of the fastener, the fastener must lend itself to robotic installation during assembly of the vehicle.